tmux died and says "no sessions" - is there any way to recover?

This sucks.

$ tmux attach-session
no sessions

My sysadmin upgraded tmux and now I can't reattach. My processes are still running according to ps ux. Is there any hope of recovering my session?

Update: There's a socket in /tmp/tmux-1234, so I tried tmux -L /tmp/tmux-1234/default attach, but tmux does nothing. Hooray.

This quickest way to determine if you can recover is:

killall -10 tmux

That will send the signal to recreate all socket files for any running tmux processes. If you're not root, no problem it will only signal your tmux process anyway.

Long story short, if tmux is not running (ps xu | grep tmux), you're screwed :(

tmux is not guaranteed to be compatible across updates; ask your sysadmin to let you know before doing upgrades or use a copy you built locally that he is less likely to mess with.